The present invention relates to a High Definition television (hereinafter, referred to as HDTV) system, and more particularly to a device and a method for providing compatibility between NTSC television and HDTV simultaneously by using a dual channel transmission system.
Since the generally adapted National Television System Committee (hereinafter, referred to as NTSC) broadcasting system has a 6 MHz bandwidth for one channel, its enhancement of resolution is greatly limited. And in order to enhance the resolution of television systems, the HDTV system is being proposed. However, even if a new channel band is assigned for the HDTV different from the NTSC broadcasting system, a drawback occurs in that the NTSC broadcast and HDTV broadcasts have to be operated separately since HDTV broadcast cannot be viewed using conventional NTSC television. To solve this drawback, a method has been proposed in which the NTSC signal is transmitted unaltered and the HDTV signal is either multiplexed on the existing NTSC broadcast signal or transmitted via a different channel. Here, the horizontal:vertical aspect ratio of the NTSC broadcast signal is 4:3 while the aspect ratio of the HDTV broadcast is 16:9. To overcome this problem of different aspect ratio composition, a side panel signal processing method and a letter box method have been proposed. In the side panel method, a the HDTV signal is output with the vertical side of the NTSC aspect ratio as the reference, and the image signal of the horizontal side is processed separately as the side panel signal and transmitted. In the letter box method, the HDTV image signal is output with the horizontal side of the NTSC aspect ratio as the reference, and there appears a black area where there is no image signal on the vertical side. Therefore, the side panel signal processing method requires complex processing procedures, and the letter box method has a drawback of poor definition.